1. Field of the Invention
The present invention relates to a sheet feeding apparatus and an image forming apparatus, and particularly, to a sheet feeding apparatus capable of conveying sheets in a separated state by blowing air to the sheets and an image forming apparatus including the same.
2. Description of the Related Art
Hitherto, an image forming apparatus such as a printer and a copying machine includes a sheet feeding apparatus which feeds sheets one by one from a sheet accommodating portion that accommodates a plurality of sheets. As the sheet feeding apparatus, there is known an air feeding type sheet feeding apparatus which blows air to an upper portion of a sheet bundle stacked on a tray so as to feed the sheets in a sorted state or in a floated state while being adsorbed onto an adsorbing and conveying belt disposed above the sheet.
The sheet feeding apparatus includes a tail end regulating member which regulates the tail end of the sheet bundle stacked on the tray and a tail end pressing member which is provided in the tail end regulating member so as to be movable in the vertical direction. The tail end pressing member is used to press the tail end portion of the sheet by a certain force, of which the tail end position is regulated by the tail end regulating member while being floated by the blown air, from the upper side of the sheet.
Here, since the tail end pressing member is provided, even when the uppermost sheet is floated by the air blowing from a leading end separating duct which is positioned at the sheet front end side, the tail end portion of the sheet may be pressed by the tail end pressing member from the upper side of the sheet. As a result, only the center portion of the uppermost sheet in the width direction is separated from a second sheet, and for example, when the separated uppermost sheet is adsorbed onto the adsorbing and conveying belt by a negative pressure, a gap is formed between the uppermost sheet and the second sheet so that the gap is blocked by the tail end portions of the sheets.
Then, since the gap is formed, air which flows along the gap flows throughout the entire area between the uppermost sheet and the second sheet. As a result, the uppermost sheet and the second sheet may be effectively separated from the leading ends of the sheet to the tail end thereof, which improves the sheet separating performance (see U.S. Patent Application Publication No. 2008/0088078 A1).
Incidentally, in the sheet feeding apparatus of the related art, when sorting air blows from the leading end of the sheet, the sheet is pressed toward the downstream side in the blowing direction, but the tail end portion is regulated by the tail end regulating plate and is pressed by the tail end pressing member from the upper side of the sheet. For this reason, when the sorting air blows from a leading end of a sheet having a small stiffness (stiffness degree), for example, a thin sheet called an ultrathin sheet having a basis weight of 50 g/m2 or less, the sheet is floated and the leading end is pressed so as to be deviated backward.
This is because the center portion of the sheet rises when the leading end of the sheet is pressed by air while the tail end is regulated due to the small stiffness of the sheet. The state is illustrated in FIG. 14. Sheets S which are stacked on a tray 12 are regulated by a tail end pressing member 17 which is provided in a tail end regulating plate 13. When sorting air and separating air blow in the directions C and D by an air blowing portion 152 to the leading ends of the sheets S stacked on the tray 12, the center portion of the floating upper sheet rises due to the small stiffness of the sheet.
Here, when the center portion rises in this way, the upper sheet is deviated backward. At this time, when the backward deviation amount of the next sheet Sb of the uppermost sheet Sa is smaller than that of the uppermost sheet Sa, the leading end of the next sheet Sb is exposed to the adsorbing portion of the adsorbing and conveying belt 21. When the adsorbing and conveying belt 21 adsorbs and conveys the sheet in this state, the adsorbing and conveying belt 21 also adsorbs the next sheet Sb together with the uppermost sheet Sa, which causes double-feeding of the sheet.
Then, when the double-feeding of the sheet occurs, a feeding failure such as skew-feeding or curling occurs on the sheet. Also, when the double-fed sheets are sent to the image forming portion, a defective image occurs. That is, when air blows to particularly thin sheets so as to feed the sheets in a separated state, there is a concern that the sheets may not be reliably fed in a separated state. Furthermore, such drawbacks also occur in a sheet feeding apparatus which sorts sheets by blowing air to a sheet bundle from the side portion thereof and feeds the sheet by a feeding roller.
Therefore, the invention is made in view of such circumstances, and provides a sheet feeding apparatus capable of feeding even thin sheets in a separated state and an image forming apparatus including the same.